MacScale (formerly USBScale) is a very easy to use application designed to offer support for various USB digital scales.

This is extremely handy in today's modern 'is it pounds or is it kilograms' world. You can place a box on the tray and know its weight in BOTH pounds and kilograms (or pounds and ounces, or grams and kilograms, etc) at the same time.

This is super-useful when comparing shipping rates from various companies, as some quote per-pound, some quote per-ounce and some quote per-kilogram.